Fig. 6. Variovorax greatly enhances the fitness of the thiamine auxotroph Cryptococcus and produce large quantities of thiamine.

a A Cryptococcus isolated from the bioreactor community is shown to be a thiamine auxotroph, whereby its optical density (OD) in minimal media increases only with the addition of thiamine. b The steady-state cell density of this Cryptococcus increases ~50-fold when grown in co-culture with Variovorax in M9 media. Variovorax too receives a fitness advantage from the interaction. c Variovorax produces large quantities of extracellular thiamine in pure culture in minimal media supplemented with 25% spent media from Cryptococcus grown in minimal media for 5 days. Error bars represent one standard deviation from the mean of n = 3 biologically independent experiments.